The present invention relates generally to components and devices in fiberoptic communication networks, and more particularly, to optical signal generators with filtered outputs which are very useful in such networks.
Most fiberoptic networks today use wavelength, or frequency, to define a communication channel in the network. These channels for such WDM (Wavelength Division Multiplexing), or more currently, DWDM (Dense Wavelength Division Multiplexing) fiberoptic networks are defined by the ITU (International Telecommunications Union) in the 1550 nm wavelength range for transmitting and receiving information over optical fibers. Depending upon the particular network, these channels are separated by differing amounts. For example, WDM networks have a 200 GHz frequency separation and the more modem DWDM networks have a narrower 100 GHz separation. In passing, it should be noted that the terms, WDM and DWDM, are meant to be used interchangeably unless clearly differentiated as in the previous sentence.
Given these defined grids of communication channels, wavelength (or frequency) conversion is a very useful operation in such networks. Signals of one wavelength (or frequency) channel can be converted to signals of another wavelength channel. One device which is emerging as a frequency converter is the difference frequency generator (DFG). The signals of the frequency to be converted are sent as input to the DFG, which also receives an energizing pump signal. The DFG converts the input signal to an output signal at a frequency dependent upon the frequencies of the input signal and pump signal. However, at the output of the device or DFG process there may be signals at both input and output frequencies due to incomplete conversion or other phenomena. It is desirable to be able to separate the input and output frequencies (or wavelengths) from each other.
The present invention provides for wavelength conversion and separation of outputs without a typical filter device which must be tuned or adjusted depending on the value of the wavelengths involved or which must be made specifically for, and hence only work properly for, a predetermined wavelength(s). This avoids complexity, provides for increased reliability and lowers costs of manufacture and maintenance.
The present invention provides for an optical signal converter which converts signals at one frequency to signals at another frequency within a frequency grid in which each adjacent pair of frequencies in the frequency grid are separated by a predetermined amount. The optical signal converter has a difference frequency generator and a separator. The difference frequency generator receives an energizing pump signal and an input signal at a first frequency and generates a converted signal at a second frequency from the input signal and the pump signal. The pump signal is set at a frequency such that the first and second frequencies are separated by an odd multiple of the predetermined amount. The separator has an input port and at least one output port with the input port connected to the difference frequency signal generator. The separator is responsive to the odd multiple separation and transmits the converted signal to the output port so that the converted signal is separated from said input signal. The optical signal converter can receive more than one input signal to generate a plurality of corresponding converted output signals. Similarly, more than one pump signal (at different frequencies but with the relationship above) can generate a plurality of converted output signals.
More specifically, if the pump frequency is such that one-half of the pump frequency is one-half between two frequencies of the frequency grid, a WDM interleaver multiplexer/demultiplexer may be used for the separator.